Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a first embodiment of a display screen or portion thereof with a graphical user interface showing our new design;

FIG. 2 is a front view of a second embodiment of a display screen or portion thereof with a graphical user interface showing our new design; and,

FIG. 3 is a front view of a third embodiment of a display screen or portion thereof with a graphical user interface showing our new design.

The peripheral evenly-spaced broken lines surrounding each graphical user interface represent an unclaimed boundary of a display screen or portion thereof and form no part of the claimed design. Within the peripheral broken lines, the evenly-spaced and unevenly-spaced broken line showing of text and other features of the graphical user interface is for environmental purposes only and forms no part of the claimed design. The difference in shading indicates a contrast of appearance and does not depict any particular color, texture, or material. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 